The Turdinae comprise the true Thrushes. These differ principally from the previous subfamilies m their larger size, in often being gregarious in the winter and in being both insectivorous and frugivorous in their diet, berries forming a considerable portion of their food.
The Thrushes are mostly migratory and a few only are resident whilst, even in these instances, they move vertically with the seasons and generally cover a very wide extent of country. The majority of them undergo a seasonal change of plumage owing to the abrasion of the edges of their feathers but these changes are never very striking and frequently hardly appreciable.
The Thrushes feed a great deal on the ground and their long tarsi enable them to hop with great speed and facility.
In structure and often in superficial resemblance many of the Turdinae resemble one another very closely and it is difficult to divide them into genera. I adhere to Oates' plan of reference to the types of coloration in making the generic divisions, especially to the colour of the under wing-coverts and axillaries.
Since Oates wrote the first edition of the Passerine birds it has been proved that the genera Myiophoneus and Arrenga are typical Thrushes in every way, the nestling being brown bird spotted and squamated in a completely Thrush-like manner.
The genus Monticola is the one in this group or subfamily of birds which comes nearest to the last subfamily and some of the members of it, such as Monticola rufogrisea, are extraordinarily like some of the Redstarts, even in size, but in India we have no species in which the resemblances are so great.
Many of the genera run into one another very closely and the natural sequence of these would seem to be Turdus, Arceuthornis, Geocichla, Oreocincla, and Zoothera.
The other genera are all well distinguished from one another and from those already mentioned.
The genus Irena, which is in many ways rather like a Thrush, I have thought better to place in a family by itself as suggested by Oberholser (Journ. Wash. Acad. Sc., vii, No. 17, October 1917).
Key to Genera.
A. Bill narrow, breadth at forehead not more than half the length of culmen; rictal bristles well developed.
a. Sexes not alike.
a1. Axillaries and under wing-coverts in
both sexes uniformly of one colour or
very nearly so; plumage never blue
nor chestnut combined with black and
blue Turdus, p. 121.
b1, Axillaries and under wing-coverts in both sexes of two strongly contrasting colours; arrangement of colours in axillaries reversed in under wing- coverts Geocichla, p. 144.
c1. Axillaries and under wing-coverts in males of one colour, in females more or less barred with two colours; plumage largely blue or bluish. .. . Monticola, p. 169.
b. Sexes alike in coloration.
d1. Axillaries and under wing-coverts entirely of one colour.
a2. Plumage in no case with any blue.. Arceuthornis, p. 153.
b2. Plumage practically wholly blue-black.
c3.Second primary as long as, or longer than, the longest secondaries
……………..Myiophoneus, p. 173.
b3. Second primary much shorter than longest secondaries…………….Arrenga, p. 182.
e1. Axillaries and under wing-coverts of two colours ; arrangement of colours in axillaries reversed in under wing-coverts.
c2. Lower plumage barred or spotted; rictal bristles tew and lateral
…………..Oreocincla, p. 157.
d2. Lower plumage squamated; rectal bristles numerous and anterior ones
projecting over nostrils Zoothera, p. 166.
B. Bill broad, breadth at forehead more than half length of culmen; rictal bristles
obsolete Cochoa, p. 183.